The invention relates to pressure-sensitive adhesive (PSA) coated articles, including tapes and transfer coatings, having microstructured surfaces and methods of making pressure-sensitive adhesive articles bearing such microstructured surfaces. The performance properties of the pressure-sensitive adhesive articles can be tailored by independently varying the microstructure and the rheological properties of the pressure-sensitive adhesive.
Repositionable pressure-sensitive adhesives, adhesives which predictably adhere to, yet remain repeatedly peelable from, a variety of target substrates over a long period of time without damaging or marring the substrate, have many commercial uses. For example, masking tapes, removable labels or office notes, protective films and medical tapes all must quickly adhere to metal, paper, plastics and skin, respectively, but must also peel smoothly away from these varied target substrates without leaving behind any adhesive residue on or harming the surface of a particular target substrate.
Several approaches have been explored in preparing and formulating repositionable adhesives. One means for providing a repositionable adhesive is through the reduction of the adhesive contact area and can be accomplished by the deposition of a discontinuous or patterned film on a backing. PCT International Appl. WO 85/04602 (Newing et al.) describes pressure-sensitive adhesive articles comprising a plurality of discontinuous adhesive segments in a pattern on at least a portion of at least one side of a carrier or backing, covering from about ten to about thirty percent of the total surface area of that carrier material. These segments have an average height of from about 15 to about 35 microns and are about 50 to about 400 microns in width. The pressure-sensitive adhesive coating used must have, according to American Society of Testing Materials (ASTM) D-3330-81, a 180xc2x0 peel of from about 0.5 to about 2.0 pound per inch (8.75 to 35 N/dm) when such adhesive is coated and evaluated as specified by this standard. Finally, the teachings of Newing et al. explicitly state that, xe2x80x9c. . . running together of the applied adhesive is to be avoided at all times . . . xe2x80x9d, as such a coalescence or coating continuity will hinder the repositionability of these adhesives.
U.S. Pat. No. 4,587,152 (Gleichenhagen et al.) describes a redetachable contact-adhesive sheet-like structure prepared by the printing of a regular discontinuous pattern of calotte-shaped (cap of sphere shaped) bonding sites up to 600 microns in diameter at their base on a backing or carrier, such bonding sites comprising an adhesive having a sufficiently high structural viscosity and thixotropy to maintain their calotte shape. Gleichenhagen et al. also teach that the adhesive properties of the claimed redetachable sheet can be altered through the variation of the height, the geometrical distribution, the frequency, and the basal diameter of the calottes. It is further asserted that the adhesive properties may be varied through controlling the viscoelastic properties of the adhesive used (i.e., adhesive ranging, xe2x80x9c. . . from very soft, highly tacky and of low shearing strength to hard, slightly tacky and of high shearing strength.xe2x80x9d). These rheological properties may be further enhanced or controlled through crosslinking the adhesive by heat or irradiation.
U.S. Pat. No. 5,194,299 (Fry) describes a repositionable pressure-sensitive sheet material comprising a sheet material bearing on one surface a discontinuous non-repetitive adhesive coating covering about 10 to about 85 percent of the surface in the form of individual adhesive islands. These islands, applied via spray coating techniques, range from about 10 to about 150 microns in height and from about 20 to about 500 microns in diameter at their bases and are comprised of a pressure-sensitive adhesive composition that, when coated continuously to a sheet material by conventional means, would not remove cleanly from a paper substrate or adherend. Fry also recognizes that the peel characteristics of the claimed sheet material may be varied by controlling the population density of the adhesive islands in the discontinuous coatings and/or the inherent tackiness of the adhesive selected for spray coating.
U.S. Pat. No. 4,889,234 (Sorenson et al.) discloses a discontinuous patterned adhesive label structure in which the level of adhesion is varied according to area of adhesive coverage on the label, the pattern in which the adhesive is coated, and the full coverage adhesive characteristics of the materials used. These variables may be adjusted independently within a single label structure, resulting in the capability to design differential peel forces at specified portions of the label. Sorenson et al. teach the criticality of selecting the adhesive material useful in the claimed structures according to their 100% coverage (i.e., continuous coating) peel force, a quantity which ranges from approximately 0.7 pound per inch (12.75 N/dm) for a solvent-type removable adhesive to approximately 6 pounds per inch (105 N/dm) for a solvent-based high strength adhesive in a 90xc2x0 peel test from a stainless steel substrate. As a point of reference in this disclosure, pressure-sensitive materials that are removable as continuous, 100% coverage coatings, as specified by the Pressure Sensitive Tape Council, have a peel force of about 2 pounds per inch (35 N/dm) or less.
Yet another approach to providing a permanently repositionable pressure-sensitive adhesive involves the use of crosslinking of a continuous, planer coating to reduce the tack and control the wetting or flow of the adhesive over the long term. U.S. Pat. No. 4,599,265 (Esmay) discloses a low tack, acrylate, removable pressure-sensitive adhesive tape which maintains peelability from a variety of ordinary target substrates. Esmay teaches that through the photocrosslinking of the tape""s adhesive layer and the use of low levels of polar monomer (up to 3% by weight of a strongly polar monomer, such as acrylic acid) along with alkyl acrylates having side chains 8-12 carbons in length in the copolymeric adhesive, the required balance of low tack, minimal adhesion buildup, and high cohesive strength can be imparted to the removable adhesive.
U.S. Pat. No. 4,693,935 (Mazurek) discloses a continuous pressure-sensitive adhesive coating composition comprising a copolymer having a vinyl polymeric backbone having grafted thereto polysiloxane moieties. An exposed surface of the PSA coating is initially positionable on a target substrate to which it will be adhered to but, once adhered, builds adhesion to form a strong bond.
European Patent Appl. 279,579 B1 (Tanuma et al.) describes pressure-sensitive adhesive sheets comprising, in one embodiment, a continuous adhesive layer xe2x80x9chaving a macroscopically non-uniform adhesion facexe2x80x9d. These pressure-sensitive adhesive constructions, formulated to exhibit both initial and long term repositionability on a variety of target substrates, attain these removable characteristics through a combination of the partial contact between adhesive layer and adherend caused by this uneven adhesive layer and through the introduction of a crosslinking structure to the adhesive to limit the adhesion build up resulting from the fluidity or flow of the adhesive over the long term. The uneven adhesive layer, according to the application, is imparted through a variety of pressing, molding, and embossing methods.
A need thus exists for a continuously coated, unfilled, microstructured pressure-sensitive adhesive article which exhibits initial repositionability when adhered to a variety of target substrates and, through the independent variation and selection of microstructured pattern and the chemical nature and rheological properties of the microstructured pressure-sensitive adhesive, displays reduced, constant or increased long-term adhesion as required by the intended application.
A need further exists for methods of preparing such microstructured pressure-sensitive adhesive articles.
The present invention relates to an article, including adhesive tapes and transfer coatings, bearing a continuous pressure-sensitive adhesive layer having a microstructured surface wherein the microstructured surface comprises a series of features and wherein the lateral aspect ratio of the features range from about 0.1 to about 10. At least two of the feature dimensions (height, width and length) must be microscopic. All three of the feature dimensions (height, width, length) may be microscopic. The microstructured patterned adhesive exhibits initial repositionability when adhered to a variety of target substrates and, through the independent variation and selection of microstructured pattern and the chemical nature and rheological properties of the microstructured pressure-sensitive adhesive, displays reduced, constant, or increased long-term adhesion as required by the intended application.
Another aspect of the present invention relates to a first method of making a microstructured pressure-sensitive adhesive tape comprising the steps of:
(a) providing a microstructured molding tool;
(b) embossing an adhesive layer of an adhesive tape comprising a backing coated with a continuous layer of an embossable pressure-sensitive adhesive with the microstructured molding tool, wherein the pressure-sensitive adhesive layer is capable of assuming the pattern of the microstructured molding tool and retaining a microstructured surface upon removal from the microstructured molding tool; and
(c) separating the microstructured molding tool from the adhesive layer to form a microstructured pressure-sensitive adhesive tape.
Another aspect of the present invention relates to a second method of making a microstructured pressure-sensitive adhesive tape comprising the steps of:
(a) providing a microstructured molding tool;
(b) coating a pressure-sensitive adhesive layer against the microstructured molding tool, wherein the pressure-sensitive adhesive layer is capable of assuming the pattern of the microstructured molding tool and retaining the microstructured pattern upon removal from the microstructured molding tool;
(c) applying a backing to the surface of the pressure-sensitive adhesive layer which is in contact with the microstructured molding tool; and
(d) separating the microstructured molding tool and the adhesive layer to form a microstructured pressure-sensitive adhesive tape.
Another aspect of the present invention relates to a third method for making a microstructured pressure-sensitive adhesive tape comprising the steps of:
(a) providing a microstructured backing having a pressure-sensitive adhesive releasing microstructured side and a planar side having less release character than the microstructured side;
(b) coating a pressure-sensitive adhesive layer on the microstructured side of the backing;
(c) adhering the surface of the pressure-sensitive adhesive layer which is in contact with the microstructured backing to the planar side of the microstructured backing; and
(d) removing the microstructured side of the backing from the microstructured surface of the adhesive layer to form a microstructured pressure-sensitive adhesive tape.
Another aspect of the present invention relates to a fourth method for making a microstructured pressure-sensitive adhesive tape comprising the steps of:
(a) providing a microstructured backing having a pressure-sensitive adhesive releasing microstructured side and a planar side having less release character than the microstructured side;
(b) coating an embossable pressure-sensitive adhesive layer on the planar side of the backing;
(c) contacting the surface of the pressure-sensitive adhesive layer which is in contact with the microstructured backing with the microstructured side of the backing to emboss the adhesive layer; and
(d) separating the microstructured backing and the adhesive layer to yield a microstructured pressure sensitive adhesive tape.
Another aspect of the present invention relates to a first method of making a microstructured pressure-sensitive adhesive transfer coating comprising the steps of:
(a) providing a microstructured molding tool;
(b) embossing an adhesive layer of an adhesive transfer coating comprising a release liner coated with a continuous layer of an embossable pressure-sensitive adhesive with the microstructured molding tool, wherein the pressure-sensitive adhesive layer is capable of assuming the pattern of the microstructured molding tool and retaining a microstructured surface upon removal from the microstructured molding tool; and
(c) separating the microstructured molding tool and the transfer coating to form a microstructured pressure-sensitive adhesive transfer coating.
Another aspect of the present invention relates to a second method of making a microstructured pressure-sensitive adhesive transfer coating comprising the steps of:
(a) providing a microstructured molding tool;
(b) coating a pressure-sensitive adhesive layer against the microstructured molding tool, wherein the pressure-sensitive adhesive layer is capable of assuming the pattern of the microstructured molding tool and retaining the microstructured pattern upon removal of the microstructured molding tool;
(c) applying a release liner to the surface of the pressure-sensitive adhesive layer which is in contact with the microstructured molding tool; and
(d) separating the microstructured molding tool and the adhesive layer to form a microstructured pressure-sensitive adhesive transfer coating.
Another aspect of the present invention relates to a third method of making a microstructured pressure-sensitive adhesive transfer coating comprising the steps of:
(a) providing a first release liner coated with a continuous layer of an embossable pressure-sensitive adhesive; and
(b) embossing the surface of the pressure-sensitive adhesive layer which is in contact with the first release liner with a microstructured second release liner to form a microstructured pressure-sensitive adhesive transfer coating.
Another aspect of the present invention relates to a fourth method of making a microstructured pressure-sensitive adhesive transfer coating comprising the steps of:
(a) providing a microstructured liner having a microstructured side and a planar side, both sides having release characteristics;
(b) coating a pressure-sensitive adhesive layer on the microstructured side of the liner;
(c) adhering the surface of the pressure-sensitive adhesive layer which is not in contact with the microstructured liner to the planar side of the microstructured liner; and
(d) removing both the microstructured side and planar side of the liner from the adhesive layer to form a microstructure pressure-sensitive adhesive transfer coating.
Definitions
The following terms are used herein.
As used herein, the term xe2x80x9cmicroscopicxe2x80x9d refers to features of small enough dimension so as to require an optic aid to the naked eye when viewed from any plane of view to determine its shape. One criterion is found in Modern Optic Engineering by W. J. Smith, McGraw-Hill, 1966, pages 104-105 whereby visual acuity, xe2x80x9c. . . is defined and measured in terms of the angular size of the smallest character that can be recognized.xe2x80x9d Normal visual acuity is considered to be when the smallest recognizable letter subtends an angular height of 5 minutes of arc on the retina. At at typical working distance of 250 mm (10 inches), this yields a lateral dimension of 0.36 mm (0.0145 inch) for this object.
As used herein, the term xe2x80x9cmicrostructurexe2x80x9d means the configuration of features wherein at least 2 dimensions of the features are microscopic. The topical and/or cross-sectional view of the features must be microscopic. The function of the pressure sensitive adhesive article is critically dependent on the form of the microstructure, which may consist of positive and negative features.
As used herein, the term xe2x80x9cpositive featuresxe2x80x9d means features projecting out of the body of the microstructured molding tool, microstructured liner, microstructured backing, or microstructured pressure-sensitive adhesive layer.
As used herein, the term xe2x80x9cnegative featuresxe2x80x9d means features projecting into the body of the microstructured molding tool, microstructured liner, microstructured backing, or microstructured pressure-sensitive adhesive layer.
As used herein, the term xe2x80x9cembossablexe2x80x9d refers to the ability of a pressure-sensitive adhesive layer to have part of its surface raised in relief, especially by mechanical means.
As used herein, the term xe2x80x9cwettingxe2x80x9d means spreading out over and intimately contacting a surface.
As used herein, the term xe2x80x9cdewettingxe2x80x9d means contracting from intimate contact with a surface.
As used herein, the term xe2x80x9crepositionable adhesivesxe2x80x9d refers to those adhesives which upon application to a specific target substrate can be removed without causing damage to the substrate and without leaving residue on the substrate and without causing damage to the backing or liner over a range of peel forces.
As used herein, the term xe2x80x9cpermanently repositionable adhesivesxe2x80x9d refers to repositionable adhesives for which the of adhesion to a given target substrate does not change substantially with time under application conditions.
As used herein, the term xe2x80x9ctemporarily repositionable adhesivesxe2x80x9d refers to those initially repositionable adhesives which build in adhesion with time, pressure or temperature such that they are no longer repositionable.
As used herein, the term xe2x80x9cself-debonding adhesivesxe2x80x9d refers to adhesives which show initial adhesion controlled by the conditions of application (pressure) and a decrease of the adhesion level with time.
As used herein, the term xe2x80x9crelease linerxe2x80x9d, used interchangeably with the term xe2x80x9clinerxe2x80x9d, refers to a thin flexible sheet which after being placed in intimate contact with pressure-sensitive adhesive surface may be subsequently removed without damaging the adhesive coating.
As used herein, the term xe2x80x9cmicrostructured linerxe2x80x9d refers to a liner with a microstructured surface.
As used herein, the term xe2x80x9cbackingxe2x80x9d refers to a thin, flexible sheet which, after being placed in intimate contact with pressure-sensitive adhesive can not be subsequently removed without damaging adhesive coating.
As used herein, the term xe2x80x9cmicrostructured backingxe2x80x9d refers to a backing with a microstructured surface.
As used herein, the term xe2x80x9ctarget substratexe2x80x9d refers to a surface to which the pressure-sensitive adhesive coating is applied for an intended purpose.
As used herein, the term xe2x80x9ctapexe2x80x9d refers to a pressure-sensitive adhesive coating applied to a backing.
As used herein, the term xe2x80x9ctransfer coatingxe2x80x9d refers to a layer of pressure-sensitive adhesive, which is not supported by a backing.